Final answer:
Ryo and Tsuruishi most likely decide to stay overnight at the inn in Tokyo because they have had to move from boarding house to boarding house to avoid harassment from the Japanese police. Staying at the inn provides them with a temporary place of refuge.
Step-by-step explanation:
In Tokyo, Ryo and Tsuruishi most likely decide to stay overnight at the inn because they have had to move from boarding house to boarding house in order to elude harassment from the Japanese police. This suggests that they are trying to find a safe and secure place to stay where they can avoid trouble. Staying overnight at the inn allows them to have a temporary place of refuge and increases their chances of evading the police.